The steroid hormone Beta-ecdysone induces morphogenesis of imaginal discs of Drosophila melanogaster under defined culture conditions. The cellular basis of morphogenesis involves a change in cell shape which may be caused by contractile proteins. Accompanying the Beta-ecdysone induced morphogenesis of discs are increases in net rRNA synthesis and incorporation of precursors into RNA, and protein. The hormone apparently induces increased or new synthesis of specific ribosomal and cytosol proteins. Mutants have been isolated which affect the ability of imaginal discs to undergo ecdysone-stimulated morphogenesis. We propose to study the uptake and distribution of ecdysone in discs and to purify and characterize ecdysone binding proteins. In addition we intend to characterize the effects of the hormone on the translation machinery in discs and to purify and characterize proteins with ecdysone-affected synthesis. Finally, we plan to study the mechanism of cellular morphogenesis utilizing ultra-structural studies, possible inhibitors of contractile protein function (cytochalasin B, colchicine, heavy water, meromyosin) and autoradiography to monitor possible differential synthesis of cell membranes. Similar studies will also be performed using mutant discs, with particular emphasis on discs with reduced or no capacity for undergoing the cell shape change, in vitro.